JAVA 单例 防止其他人new对象

[java]代码库

public class Singleton {  
    private static volatile Singleton instance = null;  
    /** 
     * 防止其他人new对象 
     */  
    private Singleton(){  
        System.out.println("init");  
    }  
    public static  Singleton getInstance(){  
        if(instance == null){  
            synchronized(Singleton.class){  
                if(instance == null){  
                    instance = new Singleton();  
                }  
            }  
        }  
        return instance;  
    }  
} //源代码片段来自云代码http://yuncode.net